1. Field of the Invention
The invention generally relates to an improved liquid cooled forged burner enclosure for holding a burner or lance to inject oxygen into an electric arc furnace during the steel making process and more particularly to a cooling arrangement for a burner enclosure surrounding a central duct for the supply of oxygen which is blown into the bath of molten steel.
2. Description of the Prior Art
In an effort to increase efficiency of the steel producing process and reduce the overall manufacturing costs, steel producers have, for the past few years, evolved to using oxidizing gases, preferably oxygen in the melting, refining, and processing steps of making steel in an electric arc furnace. Oxygen is used at different points in the melting and refining process in an electric arc furnace. Initially, it may be used to add heat during the pre-heating phase of a melt or to assist in the formation of a foamy slag during or at the end of the melting phase, and to de-carbonize the molten bath during refining. This practice has resulted in the creation of a relatively significant industry relating to the practice of injecting gases as well as solids into an electric arc steel making furnace during the steel manufacturing process.
The practice of injecting gases into a steel making furnace has progressed from mechanically controlled injectors to injectors mounted in the sidewall of a furnace to the current emerging technology of fixed position burners, that is, injectors that protrude out into the furnace in a copper “tile box”, “burner enclosure”, “nose panel”, or various other terms.
Metz et al., U.S. Pat. No. 4,369,060, discloses a plurality of agitating injectors incorporated in its refractory lining, for blowing the agitated gas, located in the bottom of the crucible, along a circle in the immediate vicinity of the sidewall of the furnace lining. Chang, U.S. Pat. No. 4,047,936, discloses imbedded concentric double-tube injectors for introducing oxygen enveloped by a shielding gas into the interior of the steel bath to oxidize impurities. Also, an overhead water cooled lance may be used to enter the vessel in the vertical position through the mouth opening. The overhead lance is attached to a rotary arm which in turn is supported by a sliding column with the lance entering the converter through a hole in the hood by rotating the arm clockwise and leaving the converter by rotating the arm counter-clockwise. Obviously, the life time of such mechanically controlled injectors or injectors built in the sidewall of the furnace itself is equal to that of the crucible and thereafter, the furnace lining needs to be rebuilt. Further, overhead water cooled lances such as disclosed by Metz, et al., while being able to be submerged directly into the molten bath to efficiently place gases and materials in a reaction zone are cumbersome and must be lowered vertically through the top of a steel making vessel. Because of their weight and size, they are not very useful to reach or be positioned for effective injection in an electric arc furnace.
These early problems evolved into the introduction of fixed position burners/injectors that protrude out into the furnace. When injecting gas into a liquid pool, it is desirable to have as much gas as possible flow into the liquid to carry out the intent/objective of the gas injection. When a nozzle of a burner lance is spaced too high above the liquid surface, then the gas impinging on the surface of the liquid will be deflected at the surface of the liquid and will not enter the liquid pool. Further, such action causes splashing of the liquid which can result in heat damage to the burner. One conventional method for reducing heat damage to a burner is to circulate a coolant such as water through the burner. Since most burners are made from copper castings or fabricated copper/steel weldments, the burner design itself is considerably more complicated to accommodate the coolant passages. Further, the cooling channels of the burner enclosure associated with the burner, due to the nature of the casting process, develop isolated “hot spots” which is an inherent design characteristic. Also, such mold design issues can cause stalling of the coolant flow in reduced service life due to wear of the casting. Also, as stated above, such burners are prone to damage as a result of the hot melt splashing on the burner tip in the harsh environment.
To avoid severe damage to the equipment, attempts have been made to recess the burner from the furnace or combustion zone. Generally, in such cases, the burner is recessed within a cavity in the furnace wall. In such arrangement, less heat or energy from the combustion zone is radiated to the burner surface and thus a coolant may not be needed by relying on the coolant passing through the furnace wall, surrounding the cavity in which the burner is recessed. Heat transfer by the radiation from the furnace decreases as the burner is withdrawn into the furnace wall cavity. However, with a burner recessed within a cavity, combustion may, and usually does occur within the cavity thus generating heat close to the burner surface and again increasing heat to the burner which may cause corrosion of the castings and reduce its efficiency. Further, if the burner is a weldment, such are prone to weld failures, which may cause water to leak into the furnace in the case of a water cooled burner. Also, recessing the burner in the furnace wall increases the distance to the molten metal, reducing its efficiency
Shver, U.S. Pat. No. 6,289,035 discloses such mounting arrangement. In Shver, the mounting block is fluid cooled to survive the hostile environment of the electric arc furnace. During the refining or decarburizing phase, the metal continues to be heated by the arc until slag forming materials combine with impurities in the iron carbon melt and rise to the surface as slag. When the iron carbon melt reaches a boiling temperature, the charged carbon in the melt combines with any oxygen present in the bath to form carbon monoxide bubbles which rise to the surface of the bath. At this point, supersonic flows of oxygen are blown at the bath with the fixed burner lance to provide a de-carbonization of the bath by oxidation of the carbon contained in the bath. By injecting the bath with oxygen, the carbon content of the bath is reduced to under two percent (2%) whereby the iron carbon melt becomes steel. The mounting block protects the burner apparatus from the harsh environment.
What is needed is a burner enclosure having an outer configuration which can be modified to fit an existing opening in the wall of an electric arc furnace. The burner enclosure provides a central passage adapted to receive a lance or burner injecting oxygen into the bath of molten metal of an electric arc furnace. The burner enclosure should not have welds on the furnace side to minimize the chance of coolant water leaking into the furnace. The coolant flow in the burner enclosure must be efficient and uniform to avoid stalling and hot spots so as to provide better heat transfer and physical characteristics over cast burner enclosures.